U.S. patent number 9,362,516 [Application Number 14/732,267] was granted by the patent office on 2016-06-07 for organic light emitting device.
This patent grant is currently assigned to Samsung Display Co., Ltd.. The grantee listed for this patent is Samsung Display Co., Ltd.. Invention is credited to Sung-Jun Bae, Kwan-Hee Lee, Ji-Hwan Yoon.
United States Patent |
9,362,516 |
Yoon , et al. |
June 7, 2016 |
Organic light emitting device
Abstract
An organic light emitting device including a plurality of
organic layers between a first electrode and an emitting layer,
wherein the organic layer includes an electron blocking layer. In
one embodiment, a first organic layer, an electron blocking layer,
a second organic layer and an emitting layer are formed on the
first electrode. The electron blocking layer has a Lowest
Unoccupied Molecular Orbital (LUMO) level which is lower than that
of the first organic layer. Thus, the electron blocking layer traps
excess electrons injected from the emitting layer, thereby
improving lifetime characteristics of the OLED.
Inventors: |
Yoon; Ji-Hwan (Yongin,
KR), Lee; Kwan-Hee (Yongin, KR), Bae;
Sung-Jun (Yongin, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Display Co., Ltd. |
Yongin, Gyeonggi-Do |
N/A |
KR |
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Assignee: |
Samsung Display Co., Ltd.
(Yongin-si, KR)
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Family
ID: |
40954473 |
Appl.
No.: |
14/732,267 |
Filed: |
June 5, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150280162 A1 |
Oct 1, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12368184 |
Feb 9, 2009 |
9054318 |
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Foreign Application Priority Data
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Feb 19, 2008 [KR] |
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10-2008-0014906 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
51/5064 (20130101); H01L 51/5096 (20130101); H01L
51/5008 (20130101); H01L 51/5012 (20130101); H01L
51/5088 (20130101); H01L 51/506 (20130101); H01L
51/5221 (20130101); H01L 51/5004 (20130101); B82Y
10/00 (20130101); H01L 51/0047 (20130101); H01L
51/5206 (20130101); H01L 51/006 (20130101); H01L
2251/301 (20130101); H01L 51/0046 (20130101); H01L
51/0059 (20130101); H01L 51/5048 (20130101); H01L
2251/308 (20130101); H01L 2251/552 (20130101); H01L
51/0077 (20130101); H01L 51/0085 (20130101); H01L
51/0072 (20130101); Y02E 10/549 (20130101) |
Current International
Class: |
H01L
51/50 (20060101); H01L 51/52 (20060101); B82Y
10/00 (20110101); H01L 51/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2000-196140 |
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Jul 2000 |
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JP |
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2005-100921 |
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Apr 2005 |
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JP |
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2006-041020 |
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Feb 2006 |
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JP |
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2006-114903 |
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Apr 2006 |
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JP |
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2007-012946 |
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Jan 2007 |
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JP |
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10-2006-0002730 |
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Jan 2006 |
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KR |
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10-2006-0108332 |
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Oct 2006 |
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KR |
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10-2007-0016662 |
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Feb 2007 |
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KR |
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WO 2004/091262 |
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Oct 2004 |
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WO |
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WO 2005/009088 |
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Jan 2005 |
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WO |
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Other References
Japanese Office action dated Sep. 13, 2011, for corresponding
Japanese Patent application 2009-036849, (3 pages). cited by
applicant .
Japanese Office action dated Jul. 10, 2012, for corresponding
Japanese Patent application 2009-036849, (2 pages). cited by
applicant .
JPO Office Action dated Apr. 16, 2013 for Japanese Patent
Application No. 2009-36849, (4 pages). cited by applicant .
JPO Office action dated Sep. 3, 2013, for corresponding Japanese
Patent application 2012-248673, (4 pages). cited by applicant .
Kato, et al., Organic Light-Emitting Diodes with a Nanostructured
Fullerene Layer at the Interface between Alq.sub.3 and TPD Layers,
Japanese Journal of Applied Physics, vol. 42, (2003), pp.
2526-2529. cited by applicant .
KIPO Office action dated Mar. 31, 2009, for priority Korean
application 10-2008-0014906. cited by applicant .
Korean Registration Determination Certificate dated Sep. 30, 2009,
for priority Korean application 10-2008-0014906. cited by applicant
.
U.S. Notice of Allowance dated Jul. 23, 2014, for U.S. Appl. No.
14/274,566, (14 pages). cited by applicant.
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Primary Examiner: Breval; Elmito
Attorney, Agent or Firm: Lewis Roca Rothgerber Christie
LLP
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application is a continuation of U.S. patent application Ser.
No. 12/368,184, filed Feb. 9, 2009, which claims priority to and
the benefit of Korean Patent Application No. 10-2008-0014906, filed
Feb. 19, 2008, the entire content of each of which is incorporated
herein by reference.
Claims
What is claimed is:
1. An organic light emitting device (OLED) comprising: a first
electrode; a second electrode; an emitting layer between the first
electrode and the second electrode; a hole injection layer between
the emitting layer and the first electrode; and an interlayer
between the emitting layer and the hole injection layer and having
a lowest unoccupied molecular orbital (LUMO) level lower than that
of the hole injection layer, wherein the interlayer is directly on
the hole injection layer.
2. The OLED of claim 1, wherein the interlayer comprises a
fullerene compound.
3. An organic light emitting device (OLED) comprising: a first
electrode; a second electrode; an emitting layer between the first
electrode and the second electrode; a plurality of hole injection
layers between the first electrode and the emitting layer; and an
interlayer between the plurality of hole injection layers, wherein
the interlayer comprises a fullerene compound, wherein the
interlayer is directly on the hole injection layer, wherein the
plurality of hole injection layers comprise a first hole injection
layer on the first electrode and a second hole injection layer on
the first hole injection layer; and wherein the interlayer is
between the first hole injection layer and the second hole
injection layer and has a lowest unoccupied molecular orbital
(LUMO) level lower than that of the first hole injection layer.
4. The OLED of claim 3, wherein the interlayer is not in direct
contact with the first electrode.
5. The OLED of claim 3, further comprising a hole transport layer
between the second hole injection layer and the emitting layer.
6. The OLED of claim 3, further comprising a first hole transport
layer and a second hole transport layer, wherein the plurality of
hole injection layers comprise a first hole injection layer, and a
second hole injection layer, and the interlayer comprises a first
interlayer between the first hole injection layer and the second
hole injection layer, a second interlayer formed between the second
hole injection layer and the first hole transport layer, and a
third interlayer formed between the first hole transport layer and
the second hole transport layer.
7. The OLED of claim 6, wherein the first interlayer has a lowest
unoccupied molecular orbital (LUMO) level lower than that of the
first hole injection layer.
8. The OLED of claim 6, wherein the second interlayer has a lowest
unoccupied molecular orbital (LUMO) level lower than that of the
first hole injection layer or the first hole transport layer.
9. An organic light emitting device (OLED) comprising: a first
electrode; a second electrode; an emitting layer between the first
electrode and the second electrode; a hole injection layer between
the emitting layer and the first electrode; and an interlayer
between the emitting layer and the hole injection layer and having
a lowest unoccupied molecular orbital (LUMO) level lower than that
of the hole injection layer, wherein the interlayer is a single
layer, and wherein the interlayer is directly on the hole injection
layer.
10. An organic light emitting device (OLED) comprising: a first
electrode; a second electrode; an emitting layer between the first
electrode and the second electrode; a hole injection layer between
the emitting layer and the first electrode; and an electron
trapping layer between the emitting layer and the hole injection
layer and having a lowest unoccupied molecular orbital (LUMO) level
lower than that of the hole injection layer, wherein the electron
trapping layer is directly on the hole injection layer.
11. The OLED of claim 10, wherein the electron trapping layer
comprises a fullerene compound.
12. An organic light emitting device (OLED) comprising: a first
electrode; a second electrode; an emitting layer between the first
electrode and the second electrode; a plurality of hole injection
layers between the first electrode and the emitting layer; and an
electron trapping layer between the plurality of hole injection
layers, wherein the electron trapping layer comprises a fullerene
compound, wherein the electron trapping layer is directly on the
hole injection layer, wherein the plurality of hole injection
layers comprise a first hole injection layer on the first electrode
and a second hole injection layer on the first hole injection
layer; and wherein the electron trapping layer is between the first
hole injection layer and the second hole injection layer and has a
lowest unoccupied molecular orbital (LUMO) level lower than that of
the first hole injection layer.
13. The OLED of claim 12, wherein the electron trapping layer is
not in direct contact with the first electrode.
14. The OLED of claim 12, further comprising a hole transport layer
between the second hole injection layer and the emitting layer.
15. The OLED of claim 12, further comprising a first hole transport
layer and a second hole transport layer, wherein the plurality of
hole injection layers comprise a first hole injection layer, and a
second hole injection layer, and the electron trapping layer
comprises a first electron trapping layer between the first hole
injection layer and the second hole injection layer, a second
electron trapping layer formed between the second hole injection
layer and the first hole transport layer, and a third electron
trapping layer formed between the first hole transport layer and
the second hole transport layer.
16. The OLED of claim 15, wherein the first electron trapping layer
has a lowest unoccupied molecular orbital (LUMO) level lower than
that of the first hole injection layer.
17. The OLED of claim 15, wherein the second electron trapping
layer has a lowest unoccupied molecular orbital (LUMO) level lower
than that of the first hole injection layer or the first hole
transport layer.
18. An organic light emitting device (OLED) comprising: a first
electrode; a second electrode; an emitting layer between the first
electrode and the second electrode; a hole injection layer between
the emitting layer and the first electrode; and an electron
trapping layer between the emitting layer and the hole injection
layer and having a lowest unoccupied molecular orbital (LUMO) level
lower than that of the hole injection layer, wherein the electron
trapping layer is a single layer, and wherein the electron trapping
layer is directly on the hole injection layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic light emitting device
(OLED) including an anode electrode, an organic layer and a cathode
electrode stacked on a substrate.
2. Description of the Related Art
Organic light emitting devices (OLEDs), which are self-emitting
devices, have wide viewing angles, excellent contrast, and quick
response, and thus have received a large amount of public
attention. Because OLEDs have low operating voltage and quick
response, and can realize multi colors, much research thereon has
been carried out.
Typically, an OLED has an anode electrode/organic layer/cathode
electrode structure. The organic layer functions as an emitting
layer (EML). In addition, the organic layer may be formed of a
plurality of layers to further include functions of a hole
injection layer (HIL), a hole transport layer (HTL) and an electron
injection layer (EIL) as well as the EML.
However, OLEDs cannot be easily applied to certain products because
reliability and lifetime (lifespan) characteristics of OLEDs are
not suitable for these products.
SUMMARY OF THE INVENTION
An aspect of an embodiment of the present invention is directed
toward an organic light emitting device (OLED) having improved
lifetime (lifespan) characteristics.
According to an embodiment of the present invention, there is
provided an organic light emitting device (OLED) including: a first
electrode, a second electrode; an emitting layer formed between the
first electrode and the second electrode; an organic layer formed
between the emitting layer and the first electrode; and an electron
blocking layer (an interlayer or an electron trapping layer) formed
between the emitting layer and the organic layer and having a
lowest unoccupied molecular orbital (LUMO) level which is lower
than that of the organic layer.
The electron blocking layer may include a fullerene compound.
The organic layer may be a hole injection layer or a hole transport
layer.
According to another embodiment of the present invention, there is
provided an organic light emitting device (OLED) including: a first
electrode; a second electrode; an emitting layer formed between the
first electrode and the second electrode; a plurality of organic
layers formed between the first electrode and the emitting layer;
and an electron blocking layer formed between the plurality of
organic layers.
The electron blocking layer may not be in direct contact with the
first electrode.
The plurality of organic layers may include a first organic layer
formed on the first electrode and a second organic layer formed on
the first organic layer, wherein the electron blocking layer is
disposed between the first organic layer and the second organic
layer and has a lowest unoccupied molecular orbital (LUMO) level
which is lower than that of the first organic layer.
The first organic layer may be a hole injection layer or a hole
transport layer.
The second organic layer may be a hole injection layer or a hole
transport layer.
The electron blocking layer may include a fullerene compound.
The OLED may further include a hole injection layer between the
first organic layer and the first electrode, wherein the first
organic layer and the second organic layer are hole transport
layers.
The OLED may further include a hole transport layer between the
second organic layer and the emitting layer, wherein the first
organic layer and the second organic layer are hole injection
layers.
The plurality of organic layers may include a first organic layer,
a second organic layer, a third organic layer and a fourth organic
layer stacked on the first electrode, and the electron blocking
layer may include a first electron blocking layer formed between
the first organic layer and the second organic layer, and a second
electron blocking layer formed between the third organic layer and
the fourth organic layer.
The first electron blocking layer may have a lowest unoccupied
molecular orbital (LUMO) level which is lower than that of the
first organic layer.
The second electron blocking layer may have a lowest unoccupied
molecular orbital (LUMO) level which is lower than that of the
first organic layer or the third organic layer, or is lower than
that of the LUMO levels of the first organic layer and the third
organic layer.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, together with the specification,
illustrate exemplary embodiments of the present invention, and,
together with the description, serve to explain the principles of
the present invention.
FIG. 1 is a cross-sectional view schematically illustrating a
structure of an organic light emitting device (OLED) according to
an embodiment of the present invention;
FIG. 2 is a cross-sectional view schematically illustrating a
structure of an OLED according to another embodiment of the present
invention;
FIG. 3 is a cross-sectional view schematically illustrating a
structure of an OLED according to another embodiment of the present
invention;
FIG. 4 is a cross-sectional view schematically illustrating a
structure of an OLED according to another embodiment of the present
invention; and
FIG. 5 is a time-brightness graph illustrating lifetime
characteristics of an OLED according to an embodiment of the
present invention.
DETAILED DESCRIPTION
In the following detailed description, only certain exemplary
embodiments of the present invention are shown and described, by
way of illustration. As those skilled in the art would recognize,
the invention may be embodied in many different forms and should
not be construed as being limited to the embodiments set forth
herein. Also, in the context of the present application, when an
element is referred to as being "on" another element, it can be
directly on the another element or be indirectly on the another
element with one or more intervening elements interposed
therebetween. Like reference numerals designate like elements
throughout the specification.
FIG. 1 is a cross-sectional view schematically illustrating a
structure of an organic light emitting device (OLED) according to
an embodiment of the present invention. Referring to FIG. 1, the
OLED according to the current embodiment of the present invention
includes a substrate, a first electrode, a hole injection layer
(HIL), an electron blocking layer (EBL), a hole transport layer
(HTL), an emitting layer (EML), an electron transport layer (ETL),
an electron injection layer (EIL) and a second electrode. Here, in
one embodiment, the ETL and/or the EIL may optionally and/or not be
included in the OLED, if desired. In addition, according to the
structure shown in FIG. 1, an organic layer, disposed between the
emitting layer (EML) and the first electrode, includes the electron
blocking layer (EBL); and, more particularly, the EBL is interposed
between the hole injection layer (HIL) and the hole transport layer
(HTL).
The substrate may be any suitable substrate that can be used in
OLEDs. In particular, the substrate may be a glass substrate and/or
a transparent plastic substrate that has high mechanical strength,
thermal stability, transparency, surface smoothness, can be easily
treated, and is waterproof. A planarization layer and/or an
insulating layer may further be interposed between the substrate
and the first electrode, if required.
The first electrode is formed on the substrate, and may be
patterned according to requirements of red, green and blue (R, G,
B) sub pixels. The first electrode is an anode in the current
embodiment, and may be a transparent electrode, a semi-transparent
electrode or a reflective electrode. A material used to form the
first electrode may be ITO, IZO, SnO.sub.2, ZnO, or the like, but
is not limited thereto. In addition, the first electrode may have a
structure having at least two layers using at least two materials
and/or other structures.
The HIL, which is an organic layer, may be selectively formed by
thermal vacuum deposition and/or spin coating. The HIL may be
formed of a material that can be suitably used to form a HIL. For
example, the material used to form the HIL may be a phthalocyanine
compound, such as copperphthalocyanine disclosed in US patent (U.S.
Pat. No. 4,356,429); a star-burst type amine derivative, such as
TCTA, m-MTDATA, and m-MTDAPB, disclosed in Advanced Material, 6, p.
677 (1994); a soluble and conductive polymer such as
polyaniline/dodecylbenzenesulfonic acid (Pani/DBSA);
poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate)
(PEDOT/PSS): polyaniline/camphor sulfonic acid (Pani/CSA);
(polyaniline)/poly(4-styrenesulfonate) (PANI/PSS); or the like, but
is not limited thereto.
For example, TCTA and m-MTDATA may be respectively represented by
Formulae 1 and 2 below.
##STR00001##
The EBL is formed on the HIL. The EBL has a lowest unoccupied
molecular orbital (LUMO) level which is lower than that of the HIL.
Accordingly, the EBL may trap excess electrons passing through the
EML. In particular, the EBL inhibits excess electrons from flowing
into the HIL, thereby improving lifetime characteristics.
The EBL needs to be formed of a material having a LUMO level which
is lower than that of the HIL. In this regard, the EBL may be
formed of a fullerene compound, for example, C60, C70, C76, C78,
C82, C84, C90, C96, or the like.
Furthermore, the EBL may be formed of a derivative of the fullerene
compound having a substituent. The substituent may be a hydrogen
atom, a halogen atom, an alkyl group, an aryl group, an alkenyl
group, a haloalkyl group, a cyano group, an alkoxy group, a dialkyl
amino group, a diaryl amino group, an aromatic cyclichydrocarbon
group, or the like.
The halogen atom may be a fluorine atom, a chlorine atom, a bromine
atom, or the like.
The alkyl group may be a straight-chain or branched-chain group
having from 1 to 8 carbon atoms such as a methyl group, an ethyl
group, a propyl group, a hexyl group, an octyl group, or the
like.
The aryl group may be an aliphatic cyclichydrocarbon group having
from 7 to 20 carbon atoms such as a benzyl group, a phenyl group,
or the like.
The alkenyl group may have from 2 to 7 carbon atoms and may be an
ethylene group, a propylene group, a butylene group, a xylene
group, or the like.
The haloalkyl group may have from 1 to 4 carbon atoms and may be a
fluoromethyl group.
The alkoxy group may be a straight-chain or branched-chain group
having from 1 to 6 carbon atoms such as an ethoxy group, a butoxy
group, a hexyloxy group, or the like.
The dialkyl amino group may have from 1 to 6 carbon atoms and may
be a dimethyl amino group, a diethyl amino group, or the like.
The diaryl amino group may have from 6 to 10 carbon atoms and may
be a diphenyl amino group, or the like.
The aromatic cyclichydrocarbon group may have from 6 to 20 carbon
atoms and may be a phenyl group, a naphthyl group, an anthryl
group, a phenanthryl group, a pyrenyl group, a perylenyl group, or
the like.
The aromatic cyclichydrocarbon group may have a substituent. Here,
the substituent may be a halogen atom, an alkyl group, an aryl
group, an alkenyl group, a haloalkyl group, a cyano group, an
alkoxy group, a dialkyl amino group, a diaryl amino group, or the
like.
For example, the C60 and derivatives thereof may include compounds
represented by Formulae 3 to 13 below.
##STR00002## ##STR00003##
In addition, the ETL may further include a material that further
lowers the LUMO level of the fullerene compound. For example, the
fullerene compound may further include an alkali metal.
Such an EBL may be formed using a wet coating method such as
thermal vacuum deposition, spin coating, inkjet printing, spray
coating and/or dip coating.
The HTL is formed on the EBL. The HTL, which is also an organic
layer, may be formed by vacuum deposition, spin coating, casting,
Langmuir Blodgett (LB) deposition, or the like. In one embodiment,
vacuum deposition is utilized because a uniform layer can be
obtained and pin holes are prevented or reduced by the vacuum
deposition. When the HTL is formed by vacuum deposition, conditions
for vacuum deposition are similar to those for the formation of the
HIL, although conditions for the deposition and coating may vary
according to the material that is used to form the HTL.
Examples of a material that can be used to form the HTL are
N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'diamine
(TPD) and N,N'-di(naphthalene-1-il)-N,N'-diphenyl benzidine
(.alpha.-NPD), but are not limited thereto.
The EML is formed on the HTL. A material that is used to form the
EML may be: a blue dopant such as oxadiazole dimer dyes
(Bis-DAPDXP)), spiro compounds (Spiro-DPVBi, Spiro-6P),
triarylamine compounds, bis(styryl)amine (DPVBi, DSA),
4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi),
perylene, 2,5,8,11-tetra-tert-butylperylene (TPBe),
9H-carbazole-3,3'-(1,4-phenylene-di-2,1-ethene-diyl)bis[9-ethyl-(9C)(BCzV-
B), 4,4-bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi),
4-(di-p-tolylamino)-4'-[(di-p-tolylamino)styryl]benzene (DPAVB),
4,4'-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi), and
bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium III
(FlrPic); a green dopant such as
3-(2-benzothiazolyl)-7-(diethylamino)coumarin (Coumarin 6)
2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)qu-
inolizino-[9,9a,1gh]coumarin (C545T), N,N'-dimethyl-quinacridone
(DMQA), and tris(2-phenylpyridine)iridium(III) (Ir(ppy).sub.3); or
a red dopant such as tetraphenylnaphthacene (Rubrene),
tris(1-phenyl-isoquinoline)iridium (III) (Ir(piq).sub.3),
bis(2-benzo[b]thiophen-2-yl-pyridine) (acetylacetonate)iridium
(III) (Ir(btp).sub.2(acac)), tris(dibenzoylmethane)phenanthroline
europium (III) (Eu(dbm).sub.3(phen)),
tris[4,4'-di-tert-butyl-(2,2')-bipyridine]ruthenium (III) complex
(Ru(dtb-bpy).sub.3*2(PF.sub.6)), DCM1, DCM2,
Eu(thenoyltrifluoroacetone)3 (Eu(TTA)3 and
butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), but
is not limited thereto. A light emitting polymer may be an aromatic
compound including nitrogen and a polymer such as phenylene,
phenylene vinylene, thiophen, fluorene and spiro-fluorene, but is
not limited thereto.
If desired, the EML may further include a light emitting host and a
light emitting dopant. The light emitting host may be a
phosphorescent host or a fluorescent host. The fluorescent host may
be tris(8-hydroxy-quinorate)aluminum (Alq3),
9,10-di(naphthyl-2-yl)anthracene (AND),
3-tert-butyl-9,10-di(naphthyl-2-yl)anthracene (TBADN),
4,4'-bis(2,2-diphenyl-ethene-1-yl)-4,4'-dimethylphenyl (DPVBi),
4,4'-bis(2,2-diphenyl-ethene-1-yl)-4,4'-dimethylphenyl (p-DMDPVBi),
Tert(9,9-diarylfluorene)s (TDAF),
2-(9,9'-spirobifluorene-2-yl)-9,9'-spirobifluorene (BSDF),
2,7-bis(9,9'-spirobifluorene-2-yl)-9,9'-spirobifluorene (TSDF),
bis(9,9-diarylfluorene)s (BDAF),
4,4'-bis(2,2-diphenyl-ethene-1-yl)-4,4'-di-(tert-butyl)phenyl
(p-TDPVBi), or the like. The phosphorescent host may be
1,3-bis(carbazole-9-yl)benzene (mCP),
1,3,5-tris(carbazole-9-yl)benzene (tCP),
4,4',4''-tris(carbazole-9-yl)triphenylamine (TcTa),
4,4'-bis(carbazole-9-yl)biphenyl (CBP),
4,4'-bis(9-carbazoleyl)-2,2'-dimethyl-biphenyl (CBDP),
4,4'-bis(carbazole-9-yl)-9,9-dimethyl-fluorene (DMFL-CBP),
4,4'-bis(carbazole-9-yl)-9,9-bis(9-phenyl-9H-carbazole)fluorene
(FL-4CBP), 4,4'-bis(carbazole-9-yl)-9,9-di-tolyl-fluorene
(DPFL-CBP), 9,9-bis(9-phenyl-9H-carbazole)fluorene (FL-2CBP), or
the like.
The amount of the light emitting dopant may vary according to the
material that is used to form the EML. However, typically, the
amount of the light emitting dopant may be in the range from about
30 to about 80 parts (or from 30 to 80 parts) by weight based on
100 parts by weight of the material used to form the EML (the total
weight of the host and the dopant). In one embodiment, if the
amount of the light emitting dopant is not within the above range,
emitting characteristics of the organic light emitting device may
decrease.
The EML may be formed by vacuum deposition, spin coating, casting,
LB deposition, or the like.
The ETL is formed on the EML. The ETL may be formed of a material
having high electron-transporting capability. Examples of the
material used to form the ETL include known ETL materials such as a
quinoline derivative, in particular, tris(8-quinolinorate)aluminum
(Alq3), TAZ, and Balq, but are not limited thereto. In addition,
the material used to form the ETL may be
bis(10-hydroxybenzo[h]quinolinato beryllium (Bebq2) represented by
Formula 14 below or a derivative thereof. The electron transporting
material may also include a metal oxide. The metal oxide may be an
oxide of an alkali metal, an alkali earth metal or a transition
metal.
##STR00004##
The EIL is formed on the ETL. However, the EIL, which facilitates
injection of electrons from the second electrode, may not be
included. The EIL may be formed of LiF, NaCl, CsF, Li.sub.2O, BaO,
or the like.
The ETL and EIL may be formed by vacuum deposition, spin coating,
casting, or the like. When the ETL and EIL are formed by vacuum
deposition, conditions for vacuum deposition are similar to those
for the formation of the HIL, although conditions for the
deposition may vary according to the material that is used to form
the ETL and EIL.
The second electrode, as a cathode electrode, is formed on the EIL.
The second electrode may be formed of a low work-function metal, an
alloy, an electrically conductive compound, or a combination
thereof. In more detail, the second electrode may be formed of Li,
Mg, Al, Al--Li, Ca, Mg--In, Mg--Ag, or the like. In addition, the
second electrode may be formed of a transparent material such as
ITO or IZO to produce a front surface organic light emitting
device.
The second electrode may be formed by vacuum deposition,
sputtering, or the like.
In the structure of the OLED having the EBL between the HIL and the
HTL as described above, the EBL can trap electrons because it has a
lower LUMO level than that of the HIL. Thus, the EBL can prevent
(or block) excess current passing through the EML from flowing into
the HIL, thereby improving lifetime characteristics.
Hereinafter, various structures of OLEDs according to embodiments
of the present invention will be described with reference to the
arrangement of a HTL between an EML and an electrode, and an EBL
between a HIL and an organic layer.
Here, the organic layers according to embodiments of the present
invention may include HIL and HTL.
Materials for each of the layers and methods of manufacturing the
layers are the same (or substantially the same) as those described
with reference to FIG. 1, and thus descriptions thereof will not be
repeated. Hereinafter, structures of the OLEDs which are different
from the structure of FIG. 1 will be described in more detail
below.
FIG. 2 is a cross-sectional view schematically illustrating a
structure of an OLED according to another embodiment of the present
invention. Referring to FIG. 2, the OLED according to the current
embodiment includes a plurality of HTLs formed between a first
electrode and an EML. That is, a first HTL is formed on the first
electrode, and a second HTL is formed on the first HTL. In
addition, an EBL is formed between the first HTL and the second
HTL.
Since the EBL has a lower LUMO level than that of the first HTL,
excess current passing through the EML is inhibited from flowing
into the first HTL.
The first HTL and the second HTL may be formed of the same material
or different materials. When they are formed of different
materials, the materials may be appropriately selected in order to
facilitate transport of injected holes to the EML.
FIG. 3 is a cross-sectional view schematically illustrating a
structure of an OLED according to another embodiment of the present
invention. Referring to FIG. 3, the OLED according to the current
embodiment includes a plurality of HILs and an EBL formed between
the first and second HILs.
In more detail, a first HIL is formed on a first electrode, an EBL
is formed on the first HIL, and a second HIL is formed on the EBL.
Then, a HTL and an EML are formed on the second HIL. The HTL may
not be formed, as desired.
Since the EBL has a lower LUMO level than that of the first HIL,
excess electrons injected from the EML are substantially trapped in
the EBL. Thus, lifetime characteristics of the OLED can be
improved.
FIG. 4 is a cross-sectional view schematically illustrating a
structure of an OLED according to another embodiment of the present
invention. Referring to FIG. 4, the OLED according to the current
embodiment includes a plurality of HILs, a plurality of HTLs and a
plurality of EBLs.
In more detail, a first HIL is formed on a first electrode, a first
EBL is formed on the first HIL, and a second HIL is formed on the
first EBL. Since the first EBL has a lower LUMO level than that of
the first HIL, excess electrons are trapped in the first EBL.
Then, a second EBL is formed on the second HIL, and a first HTL is
formed on the second EBL. Since the second EBL has a lower LUMO
level than that of the second HIL, excess electrons are inhibited
from flowing into the second HIL.
A third EBL, a second HTL and an EML are sequentially stacked on
the first HTL. Since the third EBL has a lower LUMO level than that
of the first HTL, excess electrons are inhibited from flowing into
the first HIL.
Any suitable structure is within the scope of the present invention
as long as the EBL is interposed between the HTLs, and/or the HTLs
are interposed between the EML and the first electrode. However,
the EBL should not be in contact with the first electrode and needs
to have a lower LUMO level than that of an organic layer, such as a
HTL or HIL, which is closer to the first electrode.
Hereinafter, the present invention will be described in more detail
with reference to examples evaluating lifetimes of OLEDs according
to the present invention. FIG. 5 is a time-brightness graph
illustrating lifetime characteristics of an OLED according to an
embodiment of the present invention.
An OLED according to an embodiment of the present invention
(Experimental Example) and an OLED not including an electron
blocking layer (EBL) (Comparative Example) were manufactured in
order to evaluate lifetime characteristics of the OLEDs.
EXPERIMENTAL EXAMPLE
An OLED having a structure described below was manufactured.
A corning 15 .OMEGA./cm.sup.2 (1200 .ANG.) ITO glass substrate
(Corning) was cut into pieces of 50 mm.times.50 mm.times.0.7 mm in
size, then the pieces were ultrasonic cleaned in isopropyl alcohol
and deionized water for 5 minutes for each of the pieces, and then
the pieces were washed with UV and ozone for 30 minutes to be used
as a first electrode, i.e., an anode electrode. The ITO glass
substrate was fixed in a vacuum deposition device.
Then, m-MTDATA was vacuum deposited to a thickness of 500 .ANG. on
the ITO substrate to form a HIL. C60 was vacuum deposited to a
thickness of 50 .ANG. to form an EBL. NPD was vacuum deposited on
the HIL to a thickness of 200 .ANG. as HTL. Then, an EML was formed
to a thickness of 400 .ANG. by vacuum depositing CBP as a host and
PQ2Ir(acac) as a dopant on the HTL. Then, Alq3 was deposited to a
thickness of 300 .ANG. on the EML to form an ETL, and LiF was
deposited on the ETL to a thickness of 5 .ANG. to form an EIL.
Then, Al was vacuum deposited on the EIL to a thickness of 1000
.ANG. to form a second electrode, i.e., a cathode electrode.
COMPARATIVE EXAMPLE
An OLED was manufactured in the same (or substantially the same)
manner as in Experimental Example, except that an EBL was not
formed.
EVALUATION EXAMPLE
Evaluation of Lifetime Characteristics of the OLEDs
Brightness of the OLEDs manufactured in Experimental Example and
Comparative Example was evaluated using a PR650 (Spectroscan
spectrometer, PHOTO RESEARCH INC.), and the results are shown in
FIG. 5. FIG. 5 illustrates brightness according to time when the
initial brightness of the OLEDs was regarded as 100%.
According to FIG. 5, when the brightness reliability was 90%, the
lifetime of the OLED manufactured according to the Experimental
Example was about 170 hours (a), and the lifetime of the OLED
manufactured according to the Comparative Example was about 95
hours (b). Thus, the OLED according to the Experiment Example of
the present invention has relatively longer lifetime
characteristics.
As described above, the OLED according to embodiments of the
present invention includes organic layers (e.g., HIL and/or HTL)
between the EML and the first electrode, and an EBL between the EML
and one or more of the organic layers (e.g., HIL). Thus, excess
electrons passing through the EML are inhibited from flowing into
the HIL, thereby improving lifetime characteristics.
While the present invention has been described in connection with
certain exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments, but, on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims, and equivalents thereof.
* * * * *